Hydraulic summating system

ABSTRACT

The novel hydraulic summating system disclosed in this application consists of a plurality of fixed displacement pumps, each of which supplies fluid under pressure to separate systems containing various hydraulically operated functions. The summating system includes a valve arrangement whereby the total engine power generated by the prime mover is available for one or both pumps and thus any one or all of the hydraulically operated functions has available all or a portion of the total engine power up to the maximum available.

United States Patent Symmanl; Oct. 7, 1975 [54] HYDRAULIC SUMMATING SYSTEM 3,716,308 2/1973 Kobald 417/286 3,723,026 3/1973 S land et al.

[75] Invent symmank schcfieldr 3,767,327 /1973 WZgenseil 417/216 Wis.

[73] Assignee: J. L. Case Company, Racine, Wis. Primary Examiner-Edgar W. Geoghegan Attorney, Agent, or Firm-Dressler, Goldsmith, [22] Flled' 1973 Clement & Gordon, Ltd. [21] Appl. No.: 391,064

[57] ABSTRACT 52 US. Cl. 60/420; 60/423; 60/486; The novel hydraulic Summauing System disclosed in 2 417/286 this application consists of a plurality of fixed dis- [51] Till. Cl. FB 13/09 placement pumps, each of which pp fluid under [58] F'eld of Search 4l7/286 288; /429 pressure to separate systems containing various hy- 60/420, 423, 426, 430, 431, 486; 137/100, draulically operated functions. The summating system 1 118 includes a valve arrangement whereby the total engine power generated by the prime mover is available for {56] References C'ted one or both pumps and thus any one or all of the hy- UNITED STATES PATENTS draulically operated functions has available all or a 5,154,925 11/1964 De Vita 60/429 P rti n Of the total engine power up to the maximum 3,224,196 12/1965 Bennett 60/426 available. 3,416,311 12/1968 Yoshizawa 60/420 3,695,783 10/1972 Soyland et al. 417/286 11 (3191111514 Drawmg Flgures Pu l/4P 58 52 56 011.

54 'QQ COOLER caown PRE RESER- VOIR 86' L.H.TRACK L //6 B/ 1 I26 J /3/ 1 U W j g I35 1:119 L I22) CONTROL 142 I32 4 /33 VALVE US. Patent Oct. 7,1975 Sheet 1 of3 3,910,044

061i. 7,1975 ShEet 2 of 3 3,910,Q44

U. Patent MUJOOO umjmm mmzwwmmm 50 mmmmm HYDRAULIC SUMNIATING SYSTEM This invention relates to a hydraulic drive system capable of operating a plurality of hydraulic drive members found in heavy equipment, such as, excavators, backhoes, and the like.

There are many different types of heavy construction equipment that use hydraulic drive systems for transmitting energy to the operating parts of the machinery in question. Machines of the type under discussion include a backhoe or shovel-type excavator, which basically has six main functions and several auxiliary functions. By way of example, this application will deal with the six main hydrualically operated functions of an excavator, which includes swing, crowd, tool, hoist, and the two motors for driving the separate tracks of a track-mounted excavator. It is to be understood that the novel hyorualic system disclosed herein can be utilized wherever it is desired to have a simple summating system to accomplish any combination of pressures and compensate instantly for the power requirements of multiple pump units.

In order to facilitate an understanding of the application of the novel hydraulic system, a brief description of the operation of an excavator is believed to be in order.

Generally speaking, the swing movement of an excavator requires the use of a positive displacement motor or hydraulic motor for rotating the upper structure of the excavator about a turntable and about a vertical axis. The crowd movement involves the use of one or more hydraulic cylinders that are interconnected between the boom and the dipper stick of the excavator for providing pivotal movement therebetween. The tool or bucket function also involves the use of a hydraulic drive cylinder for pivoting the bucket about a horizontal pivot point at the outer end of the dipper stick. The hoist involves the use of one or more hydraulic drive cylinders for lifting the hoist and dipper stick and pivoting them about a horizontal axis on the body of the excavator. As previously mentioned, a variety of other functions may also be performed by the use of hydraulics, but in this application, we will deal with the major ones referred to above.

As can be appreciated from the above, the operator has usually four, and often more, functions to control simultaneously. In conventional hydraulic systems for an excavator, in order to accomplish the constant speed or desired pressure, which may be required for each function, there have been utilized separate hydraulic pumps, each of which is operated by a common prime mover. In such an arrangement, obviously, the combined demand for all the pumps cannot exceed the available engine power and each of the individual pumps is provided with the capability of putting out the required level of energy to operate the particular function it is designed to control. With such a system, it is clear that the total available engine power can only be used when all of the pump and machine functions are being operated simultaneously.

Another arrangement which has been used is to employ a number of pumps, each of which is designed to handle a plurality of individual hydraulic functions. Such a system is economical in that it is designed to transmit a portion of the available engine power to a series of functions and respond in a completely modulating manner with respect to a power demand of any one, or combination of functions. In such a circuit, maximum utilization of the hydraulic energy supplied to said series of functions is accomplished. Specifically, power summation is obtained when varying pressures or flows are required of any function with respect to other functions. As applied to excavators, there have been used a pair of systems that are essentially twopump, fixed-displacement, split-horsepower systems, which function to economically summate power requirements within each of the two split power units.

Other attempts at obtaining maximum utilization of a common prime mover include very expensive, highly complicated variable-displacement pumps, but these systems are subject to the aforementioned disadvantages.

In accordance with the present invention, there is provided a novel system which in an illustrated preferred embodiment includes a plurality of fixed displacement pumps that are operated by a common prime mover. As in the previous systems, each of these pumps is set up to economically summate the power requirements of the hydraulic functions that each pump is set up to provide. However, while these systems operate in this fashion, they are further combined so that the total engine power is available to only one of the pumps or the engine power is split among the pumps according to the power demand of all of the hydraulic functions, which thus results in the total engine power being available on demand for only one or any combination of the hydraulically operated functions of the excavator. For example, if one of the systems was being used to control the hoist cylinder, tool cylinder, and one of the track motors and the on demand" requirements of that system at a given instant required the total engine power available for both pumps and the other operations of the excavator were not demanding of any of the power available by the prime mover, then the pump controlling the hoist, tool and track would have available to it the total engine power. Similarly, if one pump was called upon, for example, to supply pressure requiring two thirdsof the total engine power and the other pump one third, the novel hydraulic summating system forming the essence of the present invention would provide this mode of operation.

Thus, maximum engine power is available to all of the hydraulic functions and can be utilized at all times, even though several of the functions may not be making demands on the engine at. any given time. In effect, what is happening is that available hydraulic energy is being diverted into the system where it is needed.

Stated another way, applicants novel system incorporates all of the power demand summating features existing on current production systems where each of several pumps is used for a plurality of hydraulic functions and offers a new summation within summation power converting capability between each of the pumps. The system offers desirable constant speed of operation in such a way as to summate the power requirements of all functions simultaneously and to divert the available engine power to :any. function or combination of functions as may be dictated by the work demand of these functions. Essentially, the novel summating system provides for the total engine power to be available to each of the fixed volume pumps in the system while permitting each of the pumps to divide up the power whichever way the: demands are present.

In the illustrated embodiment, there are shown two fixed-displacement pumps, but it is to be understood that this is by way of example only.

The systems connected up to each of the pumps summate within themselves, which means that the output of the pump will go to the functions that demand the hydraulic pressure desired, but the two pumps are interconnected through a novel valving system, so that each of the pumps can collectively divide up the power available by the prime mover in whichever way the demands call for.

The novel valve system in question includes two relief valves, which may or may not be pilot operated, depending on size and other limitations. Each of these relief valves has a valve head member suject to the pressure on the high-pressure side of one of the pumps and a piston area exposed to the high-pressure output from the second pump. The valves are spring-biased and the head and piston areas are designed so that the valves will open up to by-pass some of the fluid under pressure back to the inlet of the pump when the pressures in the pump outlets reach the maximum allowable as determined by the prime mover. In the illstrated embodiment, the areas of the valve heads and pistons exposed to pump pressures are equal and thus both valves will open at the same time to bleed fluid, regardless of the pressure in each of the systems, so long as the total pressure is equal to the allowable maximum pump pressure to which the relief valves will be set.

If it is desired to have one system bleed out earlier than the other so as to maintain a minimum pressure in one of the two systems, or to maintain a fixed differential between the two systems, the valve areas and piston areas can be adjusted to accomplish this.

With this novel and efficient, but simple and inexpensive arrangement, which is accomplished by two relatively inexpensive fixed-volume pumps, oil will not be bled back to the inlet of the pump unitl the total pressure present in the system is equal to that which would bring about stalling of the prime mover. Assuming that it takes 4000 psi. before the prime mover stalls, the value areas and spring pressures are designed and set, so that oil will'not be bled back until 4000 psi. has been readed, which 4000 can be made up of 2000 psi. in one system and 2000 psi. in another, 3000 in one and 1000 in another, or 4000 in one and zero in another, or in any other combination that will be brought about by virtue of the demands on the total system.

The following description of the drawings will point out some of the advantages and is intended to be illustrative of one of the embodiments of the invention:

FIG. 1 is a pictorial view of a shovel-type excavator wherein the hydraulic system forming the substance of this invention is particularly useful;

FIG. 2 is a schematic diagram of the novel hydraulic system,

FIG. 3 is an enlarged view of the pressure relief valve; and

FIG. 4 is an enlarged view of a pilot valve used in the illustrated system.

For purposes of simplicity in describing the invention, a hydraulic drive system of the type used for operating the various funtions of a shovel-type excavator or backhoe will be described. It is to be understood, however, that the novel invention hydraulic system may be used for other types of machines having a plurality of hydraulically operated functions. Essentially, the invention, as aforementioned, is a novel summating system for summating a plurality of fixed-volume pumps being operated by a common prime mover in order to obtain the maximum power available from the prime mover, as called for bythe demands being serviced by the hydraulic pumps.

' Referring now to FIG. 1, there is shown a shovel-type excavator, generally 10, having an undercarriage l2 and an upper structure 14. The upper structure 14 is pivotally carried about a vertical axis on a turntable 16, which pivotally interconnects the undercarriage 12 to the upper structure. A hydraulic drive motor (not shown in this figure) operated by pressurized hydraulic fluid is provided for pivoting or swinging the upper structure 14 relative to the undercariage 12. Such a drive motor, or swing motor, as it will be referred to and described when describing FIG. 2, is provided for selectively swinging the upper structure 14 continuously in one direction or the other. This swinging motor is one of the basic hydraulic drive members used in the type of shovel excavator shown.

The undercarriage 12 includes a pair of drive tracks 18 for moving the excavator 10 over the ground. Each track. is driven by hydraulically-operated positivedisplacement gear motors 20, 21 driven by pressurized hydraulic fluid. Each of the hydraulic motors is independent of the other. 1

The upper structure 14 includes a cab 22 for the operator and a drive unit 24. The drive unit 24 includes an engine, such as, a gasoline or diesel engine, various hydraulic valves, oil cooler, radiator, battery, fuel tanks, etc.

A main lift boom 26 is pivotally mounted about a horizontal axis on the upper structure 14. The mounting of the axis is transverse to an offset from the main longitudinal axis of the excavator 10. A lift or hoist cylinder 28 is pivotally connected at its cylinder end to the structure 14 and at its piston end to the center portion of the boom 26. The lift or hoist cylinder 28 performs the second basic function of the excavator 10, that is, the lifting or hoisting function.

A dipper stick 30 is pivotally connected to the outer end of the boom 26 by a pivot pin 32. The pivot pin 32 is substantially parallel to the axis, which pivotally carries boom 26. A hydraulic drive cylinder 34 is pivotally connected at its cylinder end to the upper side of the boom 26 and is pivotally interconnected at its forward end to the inner end of the dipper stick 30. Drive cylinder 34 acts as the crowd cylinder, which pivots the dipper stick 30 relative to the boom 26. The crowd cylinder 34 thus performs the third basic hydraulic function of the excavator 10.

A bucket 26 is pivotally mounted at the outer end of the dipper stick 30 about a horizontal axis. A tool cylinder 38 is pivotally connected at one end to the dipper stick 30 and is interconnected to the bucket 36 through a linkage 40 at its piston end. The tool cylinder 30 pivots the bucket 36 relative to the dipper stick 30 and performs the fourth basic function of the excavator 10.

For ease of operation for an operator, it is desirable that a constant speed by provided for each of the basic functions, since this provides a more desirable habitforming method of operation. The speed is desirably substantially constant, while the power is variable.

In the excavator 10, a normal work cycle involves the use of the crowd cylinder 34 and the tool cylinder 38, or the use of the crowd'cylinder 34 and a hoist or lift cylinder 28 for the purpose of excavating. After the load has been received in the bucket, the second part in the normal sequence of operation involves simultaneously operating the hoist cylinder 28, the crowd cylinder 34, a swing motor (not shown in FIG. 1 and the tool cylinder 38 for transferring and depositing the excavated material. The third step in the sequence of operations involves the use of the swing motor, the crowd cylinder 34, the tool cylinder 38, and the hoist cylinder 28 for repositioning the bucket 36 for the next sequence of operation.

The described sequences of operation conventionally involve the use of two high-power demand functions at the same time. The functions demanding the higher power, vary in demand during the work cycle and, as is obvious to one skilled in the art, during simultaneous operation of all four of the drive members, two drive members have relatively high energy requirements and two have relatively low energy requirements. With this mode of operation in mind, it is, therefore, highly advantageous to be able to operate the items requiring the high energy requirements when the energy is called for and if these drive members happen to be operated by only one of the two pumps, then it is very important that the total engine power be available to operate the one pump responsible for the drive members requiring the high pressure.

As aforementioned, in prior hydraulic drive systems it was necessary to provide separate hydraulic pumps capable of responding to the maximum pressure of each of the drive members, which, needless to say, makes for a very expensive, very complicated system. Although improvement has been made in that it has been known to provide a plurality of pumps, each of which handles a series of functions that are summated within its individual system, there have been no systems available where there was a summating of the presssure available to the individual pumps, so that the total pressure output could be used by one of the pumps, or each of the pumps in response to demands thereon. In this way, those operations that, at any particular time happen to demand the total pressure could be serviced.

Referring now in detail to FIG. 2, there will be explained the system schematically illustrated, which explanation will consist of describing the system as if it were a split pump system, i.e., wherein a single pump is used to provide fluid under pressure for a plurality of functions, which system will summate the requirements of the functions serviced by the pump in question. Thereafter, the additional mechanisms will be described wherein the two pump systems are interrelated so they function as a totally summated system wherein any one or plurality of the functions being serviced 'by the pumps will be available to have provided to it the maximum pump pressure, or any portion thereof as required by the demands placed thereon.

Referring first to the system found on the right-hand side of FIG. 2, there is shown a supply conduit 50 containing low-pressure oil which flows into conduits 52 and 54, leading to the fixed-volume gear pumps 56, 58. As aforementioned, the system being supplied fluid under pressure from pump 56 will be first described in detail and thereafter the system being providedby fluid under pressure from pump 58 will be described. It should be noted that a prime mover, not shown, is provided for driving the gear pumps and, by wayofexam ple, we will assume that the maximum pressure being fluid to whichever side of the track motor, swing motor,

or crowd cylinder called for by the operator, which control valve is operated by control mechanisms conventional in nature and not forming a part of the present invention.

Essentially, the control valve 62 functions to determine which way the track motor is to be driven, the excavator is to swing, and the crowd cylinder is to move. As illustrated, the control valve 62 is positioned to interconnect conduit 60 with conduit 64 leading into the left-hand side of track motor 20. The outlet conduit 68 of track motor 20 interconnects with conduit 70 leadind to the upper portion of swing motor 72. The outlet of swing motor 72 communicates with conduit 74 that is interconnected to conduit 84 leading. into the piston end of crowd cylinder 34. Conduit 86 communicates with the rod end of crowd cylinder 84 andis interconnected to exhaust conduit 88 leading to oil cooler 90 and back to pump supply conduit 50. As illustrated, both the track motor 20 and the swing motor 72 are positive-displacement, gear-type motors. The. swing motor functions to cause the upper structure- ,14 to pivot about the undercarriage 12 on the turntable 16.

As was previously indicated, it is understood that the control valve 62 may alternate the pressure side of the swing motor and the track motor, so that the track may be driven in the opposite direction; or the upper structure swung in a different direction requiring the pressure fluid to be diverted from one of conduits 70, 74 to the other of conduits 70, 74. In describing the various hydraulic cylinders and motors used in the operation of the described system, movement of the particular drive member will be described as being in one direction only; however, it is to be understood that with .all the hydraulic drive motors or hydraulic drive cylinders, the operation of the appropriate control valve 1 could change the operation of the specific drive member in the reverse or opposite direction without departing whatsoever from the applicants invention.

In order to provide for summation within the system being described, each of each items, including the track motor, swing motor, and crowd cylinder, are in series.

In the hydraulic system thus far described, it is important to provide cross-over relief valves 80, 82 in by-pass conduits 76, 78 interconnecting conduits 70, 74. The cross-over relief valves actually relieve pressure from whichever conduit is under high pressure to the low pressure side at a preset pressure. The importance of these cross-over valves 80, 82 will be described hereinafter in detail.

Referring now to the left-hand side of the system illustrated in FIG. 2, there is shown the pump 58, which receives fluid from conduit 54 and pumps pressure 'fluid into conduit 100, leading to control valve 102. As

previously mentioned, the controlvalve is set to determine which conduits are interconnected, thus determining the direction of movement of the track motor 21, the tool cylinder 38, and the hoist cylinder 28, which form part of the system about to be described.

The conduit 100 is shown connected to conduit 104 leading to the left-hand track motor 21. The outlet conduit 106 is shown conected to conduit 108 which leads to the rod portion of tool cylinder 38 and the piston portion of cylinder 38 is interconnected to conduit 110 whihc connects with conduit 112 through control valve 102. Conduit 112 is connected then to the piston end of hoist cylinder 28 and conduit 114 leads from the rod end of hoist cylinder 28 back to the control valve 102 and out to conduit 116 to reservoir 118 and thereafter to supply conduit 50.

The present invention is directed to a summating system for summating the operations of both of the pumps 56 and 58, but it is important to understand the operation of the individual systems operated by each of the pumps. Each of the individual systems supplied by pumps 56, 58 summates the functions provided with fluid under pressure thereby, and the present invention in effect summates two summating systems, thereby insuring that any particular function, or functions, can have available it its whatever portion of the total pressure available it desires.

Returning now to a description of the summation of each of the individual system, it is noted that when the operator desires to operate the swing motor independently of all the other hydraulic functions, the control valve 62 can be regulated to direct the full pressure to the swing motor 72. This motor is a positivedisplacement, gear-type motor, but it cannot absorb the full pump volume, since the motor must accelerate from a stop position to a full swinging position. During acceleration, the pressure in the line 70 builds up rapidly. but since the motor cannot absorb the full pump volume, the cross-over relief valve 80 relieves from the highpressure line 70 across to the exhaust line 74. (In reverse movement of the motor 72, the relief valve 82 relieves pressure from line 74 to line 70.) TI-Ie hydraulic fluid, in the low-pressure line 74 in an amount equal to the pump volume, passes to the exhaust port of the control valve 62 and then to the oil cooler. It is to be kept in mind that in this description, the demand on the system is only coming from the swing motor. Thus, there would be no fluid under pressure directed to the crowd cylinder. When the swing motor 72 has obtained a speed which absorbs the full fluid displacement of thhe pump 56, the cross-over valve 80 closes and the full pump volume passes through the motor 72 to provide peak swing speed.

When the operator wishes to perform the crowd function independently of the other functions of the system, the pump 56 passes the pressure fluid into the control valve 62, which passes the fluid directly therethrough into communication with the crowd cylinder 34 as the piston contained within the cylinder moves the fluid in the low-pressure or exhaust side of the cylinder 34 back through conduits 86 and 88 to oil cooler 90 and supply conduit 50. When the crowd cylinder operates independently, it is capable of being powered by the full pump pressure and, depending on the demand, the prime mover will be governed accordingly.

The advantages of summating within the separate sytems, such as, the system on the right of the drawings connected to the pump 56, are when the swing and crowd functions are operated together. Thus, when the operator desires to operate the swing and crowd to pivot the upper structure of the excavator 10, the pump volume from pump 56 is first directed to the swing motor 72. However, just as when the motor 72 is operated independently, it is not possible for the motor 72 to absorb the full volume of the pump when starting from a stop position. Pressurized fluid which is not passed through the motor 72 and into the line 74, thus passes through the cross-over valve 80, which relieves at, for example, 1200 psi., so that the pressurized fluid passesdirectly from the pressure line to the exhaust side 74. The pressurized fluiid which passes through the swing motor 72, and the exhaust fluid which passes through the cross-over valve are re-united on the exhaust side of the swing motor 72. The fluid is then directed to the control valve 62, where the full pump volume passes upwardly through the conduit 84 and constant speed is provided for the crowd function, even though the swing speed is varied due to acceleration of the large mass which the swing motor 72 must move. The power torque provided by the swing motor 72 is limited by the cross-over valve 80 when the crowd cylinder 34 has a low-power demand. The power of the swing motor 72 is also limited by the cross-over valve 80 when there is a constantly varying or a high-power demand by the crowd cylinder 34. As seen, the swing motor exhaust pressure is used as the pressure which powers the crowd function. The power or torque output of the hydraulic swing motor 72 is proportional to the difference in the pressure between the pressure line 70 and the exhaust line 74. In an example, when a power demand by the crowd cylinder 34 is low, the pressure in the lines 74 and 84 is equal to, for example, 200 psi. This 200 psi. acts on the cross-over relief valve in such a way as to apply 200 psi. pressure to hold the valve 80 closed. Since 1200 psi. differnetial is required in the lines 70 and 74 to cause the pressusre in the line 70 to be relieved, this means that the pressure in line 70 must be 1400 psi. before the cross-over valve 80 relieves the pressure. When the power demand of the crowd cylinder 34 increases, the pressure increases to, for example, 400 psi. This means that the pressure must be 1600 psi. in the line 70 before the cross-over valve 80 relieves the pressure. In this way, the available swing power remains constant, even though the crowd function powered by the same pump 56 requires infinitely changing power demand.

This system provides a means of communication between the swing function and the crowd function, that is, between the swing motor 72 and the crowd cylinder 34, in such a way as to allow the available pump energy to be automatically diverted to the required demand of a particular function in direct relationship to the power demand of the second function.

From the foregoing description, it is seen that the pump 56 operates the swing motor 72 and the crowd cylinder 34, which functions are placed into direct and constant communication with each other, and the power demand of one has a direct relationship to the power demand of the other.

Referring now to the left-hand side of FIG. 2, it will be shown how this portion of the total system is also a summated system in that it will provide for operation of the tool cylinder along, operation of the hoist cylinder alone, operation of the track motor, or simultaneous operations of one or more of these elements. Specifically, it is illustrated that, as shown on the lefthand side of FIG. 2, the track motor 21, too] cylinder 38, and hoist cylinder 28 are connected up in series. The control valve 102 has been positioned to illustrate a given direction of movement of the track motor 21, downward movement of the tool cylinder 38, and upward movement of the hoist cylinder 28. As previouslly mentioned,the control valve can be adjusted to vary the direction of movement of each of these components, depending upon the operators wishes.

To operate either of these functions simulatneously, or independently, one merely has to position the control valve in the requisite manner. For example, when it would be desired to operate the track motor alone, the conduit 106 would be connected up to exhaust conduit 116. Similarly, if it is desired to operate the track motor 21 and tool cylinder 38, the pressure fluid would flow through the track motor 21, conduits 106 and 108, into the tool cylinder 38, and the exhaust side of the tool cylinder would be directed to the low-pressure conduit 116. The fluid under pressure required for whichever of the functions is being operated would be provided up to the maximum available pressure within the framework of that which can be provided-by the pump 58. It is not believed necessary to describe this system any further, since, as can be appreciated, this system will be a fully summated system in the same general manner as indicated when referring to the righthand side of the system illustated in FIG. 2.

As previously mentioned, the essence of the present invention is to be able to summate the power requirements of all of the functions described herein simultaneously and to divert the available engine power to any function or combination of functions as may be dictated by the work demand of those functions. Thus, if it is desired that the hoist cylinder and tool cylinder be provided with, for example, 4000 psi. pressure, the pump 58 would have at its disposal this pressure which exists because the available engine power is capable of producing this much pressure. Of course, it is understood that since this is the maximum pressure that is available by the engine, no pressure would be available to run any of the other hydraulically operated functions. However, if it is desired that the tool cylinder 38 and left-hand track motor 21 call for 3000 psi., then 1000 psi. would be available for the other functions, or if there was any other split, such as, 2000 psi. for the track motor 21, too] cylinder 38 and hoist cylinder 28 and 2000 psi. for the swing motor 72, track motor and crowd cylinder 34, this would also be available.

The foregoing is accomplished by incorporating in the aforementioned system a summating valve 120 which is interconnected with the high-pressure line 60 leading from pump 56 by conduit 122, and with the high-pressure line 100 leading from pump 58 by conduit 124. In the embodiment illustrated, conduit 60 is connected with conduit 122 through the action of a pilot valve 126. The purpose of providing a pilot valve is so that a relatively small summating valve can be used and yet the system will have the capability of bypassing a large amount of fluid back to the inlet side of the pump in the event the maximum pressure is reached. [t is sufficient to note at this time that the pilot valve 126 includes an orifice 130 interconnecting conduit 60 with conduit 122 and the pilot valve 126 is maintained closed by a spring 131.

There is also provided a pilot relief valve 132 which can be adjusted to open at a preset pressure to determine the maximum pressure in conduit 60. This valve can be set at whatever pressure desired and the advantage of this will be discussed hereinafter. Briefly, the

setting will be determined by spring 133, which can be adjusted by knob 134. There is a similar pilot valve 128 interconnecting conduit with conduit 124, and this valve also includes an orifice 136 interconnecting conduits 100 and 124 and a spring 137 which maintains the valve 128 closed to prevent the by-pass of fluid from conduit 100 to exhaust conduit 116. A pilot relief valve 138 similar to pilot relief valve 132 and including spring 140 and adjusting knob 142 for setting the maximum pressure in conduiit 100 is also provided. The differential areas of valves 126, 128 and the setting of springs 131, 137 determine the pressure drop across the valves 126, 128, respectively, that is required prior to opening thereof.

The specific details of the summating valve can best be seen by referring to FIG. 3. The summating valve 120 essentially consists of two pressure relief valves 160, 180, both of which are responsive to the pressure in lines 122 and 124, as will be described hereinafter.

Referring first to relief valve 160, there is illustrated a valve head portion 162 which rests on valve seat 164, blocking off the flow of fluid between conduit 124 and low-pressure exhaust conduit 176 that leads back to the inlet of pumps 56, 58. The valve stem 166 is provided at its upper end with a piston portion 168 which is in communication with conduit 122. The valve is maintained seated on seat 164 by a spring 170, the setting of which is determined by spring adjuster 172. Valve bore 174 prevents the build-up of pressure in the chamber containing spring 170.

The valve 180, as shown, is identical to valve and includes valve head 182, which seats on seat 184, blocking off the flow of fluid under pressure between conduit 122 and exhaust con;duit 176. The valve stem 186 has defined at its upper portion a piston portion 188 against which is biased a spring 190 that maintains the valve closed against the valve seat 184. The adjustment of spring 190 is provided by spring adjuster 192. Valve bore 194 prevents buildup of pressure in the chamber containing spring 190.

It is to be noted that in the embodiment illustrated, the areas 162, 168 and 182 and 188 are equal and the spring settings and 1-90 are equal and are adjusted so that when the total pressure in conduits 122 and 124 equals 4000 psi., the two valves will open to bleed hydraulic fluid back to the exhaust conduit 176. With the aforementioned identical settings, when pump overload occurs, both of the valves open to relieve the pressure in both systems.

Thus, since the valves 1 60 and will not open to bleed fluid until the total pressure in the system is equal to the maximum available pressure and since the pumps 56 and 58 are capable of putting out anywhere from zero to the maximum available pressure, any one of the functions, or any combination of the functions can have any proportion of the available pressure in the system. For example, it can be appriciated that if the tool cylinder 38 and the left-hand track motor 21 required 3000 psi., this 3000 psi. willact through conduit 100 and orifice 136 in pilot valve 128 into conduit 124 and act on valve piston area 188 and valve head area 162. Since, for the purpose of illustration the sum of these areas is equal to 1 sq. in.., there will only be a total of 3000 lbs. tending to open the valves 160 and 180, which will be insufficient (the spring being set at 4000 lbs.) and, therefore, there will be no bleeding back to the low-pressure side of the pumps. If, at the same time, there is a demand for the right-hand track -motor for 1000 psi., then this 1000 psi. is available to the pump 56 and the systems which demand the total of 4000 psi. will be operative. It is to be noted that the pumps are governed and operate in accordance'with the demand requirements placed on them by the hydraulic functions to be operated thereby.

1n the event the demand of the totally summated system exceeds 4000 psi., both halves of the system will by-pass fluid under pressure back to the inlet of the pumps unitl the pressure is returned to the total available, which, as previously mentioned in the example illustrated is 4000 psi. For example, if the demands of each pump are 2000 psi., both relief valves 160, 180 will open. 1f the demand of one pump is reduced to 1900 psi., then the allowable demand for the second pump will be increased by the same amount to 2100 psi. This would continue until one pump would have a maximum allowable of 4000 psi. As the workload demand on the lower pressure side begins to increase, the available pressure on the higher of the two will be decreased. The by-pass of high-pressure fluid to exhaust is accomplished by opening one or both of the pilot valves 126, l28'due to the drop of pressure in one or both of the chambers containing springs 131, 137. The unbalanced pressure resulting from the opening of relief valves 160 and/or 180 will result in valves 126 and- /or 128 opening to by-pass fluid to exhaust conduits 88 and/or 116.

[f it is desired to insure that each will have its own independent priority and thus when the pressure reaches the maximum limit, only the higher working pressure of the two summating valves will open to limit the available workload then the piston areas 168, 188 will be slightly less than the valve head areas 162, 182, respectively. For example, if the retaining springs 170 and 190 are adjusted to a 4000 lb. resistance and areas 162 and 182 are arranged to have 1 sq. in. of exposed surface and areas 168 and 188 has a 0.99 sq. in. of exposed surface, then areas 162 plus 168 would have 1.99 sq. in. of exposed area and 182 plus 188 would have 1.99 sq. in. respectively. If the working pressure at area 162 would be 4000 psi. and psi. at 168, the spring 170 would compress and limit the working pressure of pump 58 to 4000 psi. At the same time, the 4000 psi. of pump 58 would be usbjected to the 0.99 sq. in. of area 188, which would result in a load of 3990 lbs. on the spring 190, which is preset at 4000 lbs. the retaining force being higher than the laod would insure that the valve 180 would remain in the closed position, thereby giving priority to the lower operating pressure of either pumping unit. As the demand of the lower working pressure would increase, the allowable pressure of the higher demand would decrease until both demands would become equal, at which time both relief valves would open. The combined areas of each poppet being 1.99 sq. in. which is retained by the 4000 lb. spring force would result in a pressure limit of 2010 psi.

It is to be noted that while in the embodiment illustrated the summating valve 120 is designed so that both valves 160, 180 open at the same time, the invention is obviously not limited to this arrangement. For example, if it is desiried to insure that a certain minimum pressure is maintained in, for example, conduit 124, so that the pressure in hoist cylinder 28 cannot go below a certain level, the designs of the valves 160, 180 will be adjusted and springs set accordingly to insure that the valve .l60- controlling the flow between conduit 124 and-exhaust conduit 176 will not open unless the pressure in conduit 1.24} exceeds that pressure required to maintain the hoist cylinder in, the desired position.

, Another way to accomplish predetermined priorities is to vary the setting of the pilot relief valves 132, 138. For example, by setting the pilot relief valve 138 to open at 3000 psi., it is assured that the system fed by pump 56 will always have available to it a minimum of 1000 psi. (assuming a total maximum of 4000 psi.). If, however, the work load requirement fed by pump 56 increases to 1200 psi., then the available 3000 psi. for the system fed by pump 58 would be reduced to 2800 psi. This could continue until a balance pressure requirement was reached at 2000 psi. availability for both pumping units simultaneously.

It can be appreciated by one skilled in the art that the springs, piston, valve head areas, and pilot relief valves can be adjusted to provide for a variety of operating conditions.

METHOD OF OPERATION In order to facilitate an understanding of the system disclosed in FIG. 2, the following method of operation is set forth.

Assuming that the maximum output of the pumps 56, 58 is equal to 4000 psi., the hydraulically operated components can be adjusted to use whatever portion of this pressure is available. If, for example, the track motor 20, swing motor 72 and crowd cylinder 74 require 2000 psi., the right-hand pump 56 will be governed to provide this pressure. Similarly, if the lefthand track motor 21, tool cylinder 38, and hoist cylinder 28 require 2000 psi., the pump 58 will be available to supply it, since the prime mover (not shown) is capable of producing 4000 psi.

The relief valves and will remain closed, since they are set to open when the total pressure to which they are exposed exceeds 4000 psi.

By way of an example, if the available power from the prime mover could drive two fixed displacement pumps of known volume at 2000 psi. and the left-hand track drive motor 21 has a demand of pump 58 for only 1000 psi., then the pressure limiting summation valve 120 would instantly re-adjust to an available total work load of 3000 psi. for pump 56. This available pressure could be used for any combination of demands resulting from the work load of the right-hand track drive motor 20, the swing motor 72, or the crowd cylinder 34, and all functions would retain a constant speed, with the exception of the swing drive motor that could be accelerating or decelerating, but retaining its predetermined constant torque.

A still further example is a situation in which the work load of both track drive systems requires an equal pressure of 2000 psi., which, for the purpose of illustration, would be the maximum available from the prime mover. If either track drive requires a lesser pressure, the reduction of its requirement is instantly added to the availability of the opposite driveby increasing the pressure relief allowed for the higher load requirement. This sytem is particularly important in a power turn, where one track drive is locked, requiring no work load, and the demand of the opposite track demands full power from the prime mover. In this case, the summating pressure unit would increase the allowable pressure for the heavily loaded drive from 2000 psi. to 4000 istics of each track drive with respect to the other.

It can be readily appreciated from the above that any combination is available in a system where the system permits total summating of all the units utilizing output pressure from fixed displacement pumps. As previously mentioned, where the summator consists of two relief valves that are identical when the .pressure demands exceed the total consisting of, for example, 4000 psi., the relief valves 160, 180 will open to by-pass fluid under pressure to the reservoir. In this case, the opening of the valves will reduce the pressures in the spring chambers of the pilot valves 126, 128, resulting in the pilot valves opening and by-passing large quantities of fluid under pressure back to the inlet of the pumps. However, as previously mentioned, the releif valves 160, 180 can be made slightly different with one valve having a priority over the other, whereby only one of the valves will open to bleed excess pressure.

Also within the scope of this invention a system employing a number of pumps in excess of two, in which case the valves forming part of the summating valve system will increase by a like amount. In such a situation, the valves would be designed to have a plurality of areas exposed to fluid pressure from the outlet of each of said pumps and will operate in a manner similar to that herein described. Also, the valves can, of course, be designed to maintain a minimum of pressure in one system, or the other, which was discussed earlier in the specification. Furthermore, while the system illustrated in the drawings includes two pumps 56, 58 having an output pressure equal to the maximum available from the prime mover, this need not be the case. For example, one of the pumps could be much smaller than the other, which would, of course, limit its output, but as long as at least one of the pumps is capable of taking the full output pressure from the prime mover, such a system would encompass the present inventin.

It is, of course, intended to cover by the appended claims all such modifications as fall within-the terms thereof.

What is claimed is:

l. A summating system for providing the requisite pressurized fluid for one or more hydraulically operated functions including a prime mover, a plurality of fixed displacement pumps, each of which provides fluid under pressure in a system to operate a plurality of functions, at least one of which pumps is capable of utilizing the total output of said prime mover, relief valve means responsive to the sum of the pressures in the systems supplied by each of said pumps, whereby at least one of said pumps can utilize the total output of said prime mover or any portion thereof as determined by the demands of the hydraulically operated functions supplied thereby, said relief valve means functioning to relieve the pressure in one or more of said systems when the sum of the presures in the system exceeds the maximum allowable pressure.

2. A summating system for insuring that the various demands of hydraulically operated functions receive the required pressurized fluid to accomplish their.intended functions on demand, including a prime mover, first and second constant displacement pumps having fluid inlets for receiving low pressure fluid and outlets containing pressurized fluid, each of said first and second pumps being part of a separate system to provide fluid under pressure to a plurality of hydraulically operated functions, pressure relief valve means responsive to thefluid under pressure in the outlet conduits of each of said pumps, eachof said, relief valve. means including spring-biased valves controlling the flow of fluid under pressure between the outlet and inlet conduits of each of said pumps, each of said valves having a valve head exposed to the'pressure in the outlet conduit of one of said' pumps and an additional area exposed to the pressure in the outlet conduit of the other of said pumps whereby when total force exerted of each of said valves exceeds the presetting thereof-at least one of the valves will open to return the sum of the pressures in said outlet conduits to the total maximum allowable pressure as predetermined by said prime mover.

3. A system as set forth in claim 2, wherein the relief valves set forth each has a valve head portion closing off the flow to the inlet of said pumps, which head portion is exposed to and controls the flow from the highpressure conduit of one of said pumps, and a piston area exposed to the fluid under pressure in the outlet conduit of the other of said pumps.

4. A system as set forth in claim 2 in which one of said pumps is positioned to regulate the flow of hydraulic fluid under pressure in a system controlling a first track motor, swing motor, and crowd cylinder of a hy draulically operated excavator and the other of said pump controls the fluid under pressure in a system which controls a second track motor, hoist cylinder, and tool cylinder.

5. A system as set forth in claim 4 in which the first track motor, swing motor, and crowd cylinder functions are serially disposed and the second track motor, hoist, and tool cylinders are also located in series.

6. A system as set forth in claim 2 including pilot means for controlling the flow between the highpressure conduit of each of said pumps and one of said relief valves, whereby small relief valves can be utilized while insuring that there can be rapid by-pass of fluid under pressure from said high-pressure conduits in the event the maximum allowable pressure in the system exceeds that which has been determined by the setting of said relief valves.

7. A summating valve assembly for controlling the fluid under pressure in systems supplied by fixed displacement pumps including a relief valve for each of said pumps, which valves are responsive to the fluid under pressure emanating from all of said pumps, sid valves controlling the flow of fluid between the outlet and inlet of said pumps to relieve the pressure in the systems when the summated outlet pressures of said pumps exceed the maximum allowable pressure.

8. A valve assembly as set forth in claim 7 in which each valve is a spring-biased relief valve in which the setting thereof equals the maximum allowable force permitted to act on the valve which is equal to the exposed valve area multiplied by the pressures existing in the systems supplied by said pumps.

9. A valve assembly as set forth in claim 8 in which the system consists of two fixed displcement pumps and thus there are provided two valaves, each of which has a valve head portion exposed to the output of one of the fixed displacement pumps and a piston portions exposed to the output pressure of the other of said fixed displacement pumps.

10. A summating system for providing the requisite pressurized fluid for one or more hydraulically operated functions including a prime mover, a pluraltiy of fixed displacement funtions each of which provides fluid under pressure in a system to operate a plurality of functions, but each being capable of utilizing a total output of said prime mover, relief valve means responsive to the sum of the pressures in the systems supplied by each of said pumps, whereby each of said pumps can utilize the total output of said prime mover or any portion thereof as determined by the demands of the hydraulically operated functions supplied thereby, said relief valve means functioning to relieve the pressure in said system when the sum of the pressures in the systems exceeds the maximum allowable pressure.

11. A summating system for providing the requisite pressurized fluid for one or more hydraulically operated functions including a prime mover, a plurality of 16 fixed displacement pumps, each of which provides fluid under pressure in a system to operate a plurality of functions, but each being capable of utilizing a total output of said prime mover, relief valve means responsive to the sum of the pressures in the systems supplied by each of said pumps, whereby each of said pumps can utilize the total output of said prime mover or any portion thereof as determined by the demands of the hydraulically operated functions supplied thereby, said relief valve means including a relief valve for each 01 said pumps and defining areas reaponsive to the fluid under pressure emanating from each of said pumps and functioning to relieve the pressure in one or more of said systems when the sum of the pressures in the systems exceeds the maximum allowable pressure. 

1. A summating system for providing the requisite pressurized fluid for one or more hydraulically operated functions including a prime mover, a plurality of fixed displacement pumps, each of which provides fluid under pressure in a system to operate a plurality of functions, at least one of which pumps is capable of utilizing the total output of said prime mover, relief valve means responsive to the sum of the pressures in the systems supplied by each of said pumps, whereby at least one of said pumps can utilize the total output of said prime mover or any portion thereof as determined by the demands of the hydraulically operated functions supplied thereby, said relief valve means functioning to relieve the pressure in one or more of said systems when the sum of the presures in the system exceeds the maximum allowable pressure.
 2. A summating system for insuring that the various demands of hydraulically operated functions receive the required pressurized fluid to accomplish their intended functions on demand, including a prime mover, first and second constant displacement pumps having fluid inlets for receiving low pressure fluid and outlets containing pressurized fluid, each of said first and second pumps being part of a separate system to provide fluid under pressure to a plurality of hydraulically operated functions, pressure relief valve means responsive to the fluid under pressure in the outlet conduits of each of said pumps, each of said relief valve means including spring-biased valves controlling the flow of fluid under pressure between the outlet and inlet conduits of each of said pumps, each of said valves having a valve head exposed to the pressure in the outlet conduit of one of said pumps and an additional area exposed to the pressure in the outlet conduit of the other of said pumps whereby when total force exerted of each of said valves exceeds the presetting thereof at least one of the valves will open to return the sum of the pressures in said outlet conduits to the total maximum allowable pressure as predetermined by said prime mover.
 3. A system as set forth in claim 2, wherein the relief valves set forth each has a valve head portion closing off the flow to the inlet of said pumps, which head portion is exposed to and controls the flow from the high-pressure conduit of one of said pumps, And a piston area exposed to the fluid under pressure in the outlet conduit of the other of said pumps.
 4. A system as set forth in claim 2 in which one of said pumps is positioned to regulate the flow of hydraulic fluid under pressure in a system controlling a first track motor, swing motor, and crowd cylinder of a hydraulically operated excavator and the other of said pump controls the fluid under pressure in a system which controls a second track motor, hoist cylinder, and tool cylinder.
 5. A system as set forth in claim 4 in which the first track motor, swing motor, and crowd cylinder functions are serially disposed and the second track motor, hoist, and tool cylinders are also located in series.
 6. A system as set forth in claim 2 including pilot means for controlling the flow between the high-pressure conduit of each of said pumps and one of said relief valves, whereby small relief valves can be utilized while insuring that there can be rapid by-pass of fluid under pressure from said high-pressure conduits in the event the maximum allowable pressure in the system exceeds that which has been determined by the setting of said relief valves.
 7. A summating valve assembly for controlling the fluid under pressure in systems supplied by fixed displacement pumps including a relief valve for each of said pumps, which valves are responsive to the fluid under pressure emanating from all of said pumps, sid valves controlling the flow of fluid between the outlet and inlet of said pumps to relieve the pressure in the systems when the summated outlet pressures of said pumps exceed the maximum allowable pressure.
 8. A valve assembly as set forth in claim 7 in which each valve is a spring-biased relief valve in which the setting thereof equals the maximum allowable force permitted to act on the valve which is equal to the exposed valve area multiplied by the pressures existing in the systems supplied by said pumps.
 9. A valve assembly as set forth in claim 8 in which the system consists of two fixed displcement pumps and thus there are provided two valaves, each of which has a valve head portion exposed to the output of one of the fixed displacement pumps and a piston portions exposed to the output pressure of the other of said fixed displacement pumps.
 10. A summating system for providing the requisite pressurized fluid for one or more hydraulically operated functions including a prime mover, a pluraltiy of fixed displacement funtions each of which provides fluid under pressure in a system to operate a plurality of functions, but each being capable of utilizing a total output of said prime mover, relief valve means responsive to the sum of the pressures in the systems supplied by each of said pumps, whereby each of said pumps can utilize the total output of said prime mover or any portion thereof as determined by the demands of the hydraulically operated functions supplied thereby, said relief valve means functioning to relieve the pressure in said system when the sum of the pressures in the systems exceeds the maximum allowable pressure.
 11. A summating system for providing the requisite pressurized fluid for one or more hydraulically operated functions including a prime mover, a plurality of fixed displacement pumps, each of which provides fluid under pressure in a system to operate a plurality of functions, but each being capable of utilizing a total output of said prime mover, relief valve means responsive to the sum of the pressures in the systems supplied by each of said pumps, whereby each of said pumps can utilize the total output of said prime mover or any portion thereof as determined by the demands of the hydraulically operated functions supplied thereby, said relief valve means including a relief valve for each of said pumps and defining areas reaponsive to the fluid under pressure emanating from each of said pumps and functioning to relieve the pressure in one or more of said systems when the sum of the pressures in the systems exceeds the maximum allowaBle pressure. 